Bauxite-digester.



' l HENRY HOWARD, or BnooKLINE, MASSACHUSETTS,

BAUXITE-DIGESTER.

To all :whom it may concern Y `Be 1t known that I. HEXRYHOWARD, a

`citizen of the United States, resi-ding at Brookline, in the" county of Norfolk and State of Massachusetts, have invented certaln new --a:nd use-ful` Improvements 1n BauXite-Digesters, of which the following is a speciiication.`

This invention. 1s an apparatus for digestf v ing bauxite in strong solutions'ot` caustic soda1 forthepreparation of aluminate solu- 1 tions.

In the. preparation of aluminate solutions, as 1n lthe well-known Bayer process, the

bauxite'jis digested in caustic soda solutions of 42 tp 47 Baume, under a `pressure of' 40' :to 70 pounds per vsquare inch. Ihis neces sitates the use of steam at. Vcomparatively high pressures, say 150 to 250 pounds per square 1nch,"rendermg it diflicult and dann garous, as well as uneconomlcal. to employ jacketed vessels,V and making it impracti- "cable te construct them in large units.

vMoreovr, the character of the solvent and v02E-the solution is such that it is extremely difficult to maintain" any joints below the liquid ievei;

` 4'The present invention provides a form of digester in which the requisite, temperatures' and pressures may be maintained economically and without diiiiculty or danger= which is freefrom tendency to leakage. of which the contents may be freely circulated, and

which maybe easily and safely constructed in very large units. v

A preferred embodiment of the invention is illustrated in the accompanying drawing,

i wherein the figure is a central vertical secvide 4an upward path for tion. v l.

The apparatus `illustrated comprises a strong steel vshell l, properly riveted and calk'ed` and completely covered by a heat,- insulating -jacket 2. The steam coil 3 is located within theshell, concentric therewith.l and spaced from the verticalwalls to prothe circulating liquor..V This coil is constructed of seamless 'trrbing'f the lengths being welded together,

and welded to vthe fiangesfl, which are riveted to the shell. The turns of the coil are `lsupported within the shell b vstandards 5 '1 carriedby the shell, in such` manner that the coil is entirely free. to'expand and contract withoutcommunicatingstrains to the shell.

A val'ved inlet opening for the charge is provided atfG, and a manhole at 7, both in Specification of Letters Patent.

PatentedMar. 14, 1916.

Application mea :une 24, 1914. sera-.11m 847,163.

'pressure within the digester is utilized to ele 'ate the solution to avoid pumping.

A vertical `shaft 11 carrying propeller 4blades 1Q enters the digester through astuiiy lng-box and bearing 13 in the center of the cover, and is hung in suitable external bearings not shown. The propeller 12 is a circulating device: in contradistinction to an agitator, andis"preferably rotatable in such dlrection as to circulate the charge down- 'ardly inthe central regionof the digester and kupwardly around its periphery and in contact with the steam coil 3. This circula tion is preferably rendered more definite hy providing.y an open-ended cylindrical casing 1i. suitably supported within the coil 3 and encircling the propeller 1Q.

This Vapparatus has successfully solved one of the serious engineering diiiiculties which have been encountered yfor many years inthe practice o the 'Bayer process.

I claim':-

l. An apparatus for digesting bauxite -with alkaline solutions. coml'u'ising a closed vessel adapted to withstand heavy internal pressures and provided with a heat-retain ingr covering, a steam coil mounted in proximity to the shell of the vessel, said co-il supported from said shell but free to move relatively thereto. and an'axial rotary circulating device constructed to maintain a definite circulation of the contents of the vessel.

2. An apparatus for digesting bauxite with alkaline solutions: comprising a closed vessel adapted to withstand heavy internal pressures and provided with a heat-retaining covering` a steam coil mounted in prox'- imity to the shell of the vessel, said coil supp'ortcd from said shell but free to move relatively thereto. and an axial rotary circulating device V'constructed to maintain a definite circulation of the contents of the vessel, said device comprising an openfended casing within the steam coil, and a rotary propeller Aarranged to circulate the contents of the vessel downwardly through said casing and up'- wardly over said coil.

3. An apparatus for ydigesting bauxite ing covering: a steam coil mounted in prox` iiiity to the shell of the vessel and practi` cally the entire height thereof, said coil slipported from said shell but free to move rela tively thereto, and an axial rotary circulating device constructed to maintain a definite "j circulation of the contents of the vessel.

4. An apparatus 'for digesting bauxite with alli-aline solutions, comprising a closed vessel adapted to withstand heavy internal pressures and provided with a heat-retaining covering, a steam. coil mounted in proxiiiiit'v to the shell of the 'vesseliand practically the entire height thereof, said coil sup-A ported from said @hell but free to move relatively thereto, and mi axial rotary circulating device constructed to maintain a definite circulation of the contents of the vessel, said device comprising fan operi-ended casing JWithinthe steam coil near the bottom tliereof, and a rota-ry propeller larranged to cii cur'late the contents of the vessel downwardly through said casing and upwardly over said coil.

In testimony whereof I affix my-.signature 2,5

Witnessesr l:HENRY Witnesses r THos. J. SHAiiixroia,4

MAE lV. QBiiEN., 4

in presence of tlwo 

